1. Field of the Invention
The present invention relates to a foldable radio communication apparatus which has a pair of housings in which a circuit board is housed.
2. Description of the Related Art
Radio communication apparatuses of this type have been employing a structure that enables conduction of an electric current, which is induced in a pair of circuit boards, to be improved and obtains an antenna gain as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2004-040524 and Japanese Unexamined Patent Application Publication No. 2006-086715.
FIG. 17 is a front view showing a radio communication apparatus according to a first related-art example. FIG. 18 is a perspective view showing a radio communication apparatus according to a second related-art example.
In a radio communication apparatus 100 disclosed in Japanese Unexamined Patent Application Publication No. 2004-040524, as shown in FIG. 17, ground units 111 and 121 of a pair of circuit boards 110 and 120 are connected via a resonant circuit 130. The resonant circuit 130 is a circuit in which a series-connected component and a resonance-use conductor 133 serving as an inductor are connected in parallel. In the series-connected component, a resonance-use conductor 131 serving as an inductor and a capacitor unit 132 are connected in series.
This causes a high-frequency electric current induced in the circuit board 110 by an antenna operation of an antenna 101 to flow to the circuit board 120 through the resonant circuit 130. An antenna gain is increased by making the conduction state of the high-frequency electric current be in a favorable state by using an impedance of the resonant circuit 130.
On the other hand, a radio communication apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2006-086715, as shown in FIG. 18, has a structure in which a helical antenna 201 is provided at a front side of a conductor portion 210 of a circuit board and a flip element 230 is provided between the antenna 201 and the conductor portion 210. With such a structure, an electric current which flows into the flip element 230 from the conductor portion 210 is led using the flip element 230 in the direction opposite to the flow of the electric current in the conductor portion 210, and thus an antenna gain is increased.
However, existing radio communication apparatuses described above have the following problems.
First, in the radio communication apparatus shown in FIG. 17, the resonant circuit 130 includes the series-connected component in which the resonance-use conductor 131 serving as an inductor and the capacitor unit 132 are connected in series, and thus an electric current at the time of resonance always flows through both the resonance-use conductor 131 serving as an inductor and the capacitor unit 132. Thus, resonance is caused with an electric current having a desired frequency only if a condition regarding both the resonance-use conductor 131 serving as an inductor and the capacitor unit 132 is satisfied. Therefore, the impedance of the resonant circuit 130 can be controlled within only a specified and narrow range of frequency, and impedance control over a wide range of frequencies is difficult.
Next, the radio communication apparatus shown in FIG. 18 needs the helical antenna 201, which extends outside, and the flip element 230, whereby there is a problem that the physical volume of the radio communication apparatus becomes large.